Furnace replacement: what, when and how
Furnace replacement makes sense when the unit is old, repair bills keep coming back, or a failure such as a cracked heat exchanger makes it unsafe to run. Planning the swap before a cold snap gives you time to compare efficiency, fuel type and quotes instead of buying in a hurry.
When does a furnace need replacing?
Age is the first filter. Many furnaces run for roughly fifteen to twenty years with regular service, and the figure for your own model is in the manual. Past that point parts get harder to find and each call-out is a bet on the next one. Our guide to heating system lifespans in Canada shows how furnaces compare with boilers and heat pumps.
Age alone is not a verdict. A well-kept unit can be worth keeping, and a young one with a bad design may not. The pattern of failures matters more.
What are the signs of a failing furnace?
Some signs point to a fix, others to a full swap.
- Frequent repairs. Two or three service calls in a few winters usually mean the money is better spent on a new furnace.
- Rising energy bills. A tired burner and blower lose efficiency, so the same house costs more to keep warm.
- Uneven heating. Cold rooms next to hot ones can come from the furnace, the ducts, or both.
- Noise and short cycling. Banging, rattling or a furnace that cycles on and off every few minutes is wearing out.
- A cracked heat exchanger. This is a safety problem, because combustion gases can reach the house air. It is normally the point where replacement beats repair.
If a carbon monoxide alarm sounds or you smell fuel, leave the house and call the utility or emergency services first. The repair or replace decision guide goes deeper on the cost side.
Which type of new furnace should you choose?
Most Canadian homes with gas service choose between a mid-efficiency and a high-efficiency model. High-efficiency furnaces condense water vapour out of the exhaust and need plastic venting and a drain, which is part of why they cost more to install. The efficiency figure is the AFUE rating: it states what share of the fuel becomes heat in the house over a season. A higher number means lower fuel use for the same warmth.
Two other choices shape comfort. A single-stage burner is either on or off, while two-stage and modulating versions match output to the weather and run quieter with steadier temperatures. A variable-speed blower does the same for airflow. Electric furnaces and oil furnaces exist for homes without a gas line, and the trade-offs between energy sources are compared in natural gas versus electric heating.
It is also the moment to ask whether a heat pump should take over part of the job. The heat pump versus furnace guide sets out when that pairing pays off.
What do furnace replacement costs depend on?
The furnace itself is only one line on the quote. Capacity, efficiency tier, venting changes, ductwork repairs, a new thermostat and the permit all move the total, and so do region and season. Prices shift from year to year, so no national number is reliable. The cost breakdown explains each driver, and the guide to reading a furnace quote shows what to compare line by line.
Size deserves attention. A furnace should match the heat loss of the house as it is today, not the unit that was installed decades ago. After new windows or insulation, the old size is often too big, and an oversized unit short cycles, wastes energy and wears out sooner. A proper load calculation is the right basis.
How does a furnace replacement work?
Most jobs follow the same order. A licensed contractor inspects the old unit, the venting, the gas or electrical connection and the ducts, then quotes in writing. After you accept, the installer books a date, and the work needs a permit in most municipalities.
On the day, the old furnace is shut off, disconnected and removed, the new one is set in place, and gas, venting, electrical and condensate lines are connected. The system is then tested, and the installer should show you the filter, the thermostat settings and the shut-offs. A typical swap takes a day, and longer when venting or ductwork changes. A fuller walk-through is in what to expect on installation day.
Get the warranty terms in writing: parts, labour and any registration step.
Quick answers
How long does a furnace last?
Roughly fifteen to twenty years with regular maintenance, though it depends on the model, the installation and the climate. The manufacturer's documentation for your unit gives its own figure.
Is it better to repair or replace an old furnace?
Replacement tends to win when the unit is near the end of its expected life, service calls are frequent, or the heat exchanger is cracked. One cheap fix on a younger furnace rarely justifies a swap.
Are there rebates for a new furnace?
Programs for heating equipment change often and depend on the province, the utility and the energy source. Check the Government of Canada energy-efficiency pages, your provincial energy ministry and your gas or electric utility for the current terms.
Can a heat pump replace a furnace?
In many homes a cold-climate heat pump can carry most or all of the heating load, sometimes with the furnace kept as a backup. A contractor's load calculation shows whether it fits your house.